pku2157 Maze (搜索)

 迷宫中有钥匙和门，收集到钥匙能打开对应的门，问能否走出迷宫，

这里的算法是多次广度优先搜素，每次广度优先搜索收集钥匙，看能否走到目的地，如果走不到目的地，则拿出收集到的钥匙打开门，继续广度优先搜索。 如果钥匙收集完了，到不了目的地，也打不开新的门，说明无解。

 

#include <iostream> #include <queue> using namespace std; int keynum[5], keyfound[5]; int m, n, srcx, srcy; char tmap[20][20]; bool visited[20][20], opened[5];; int dir[4][2] = {​{0, 1}, {0, -1}, {1, 0}, {-1, 0}}; struct POINT { int x; int y; } cur, next; bool bfs() { queue<POINT> q; int i; char ch; cur.x = srcx; cur.y = srcy; visited[srcx][srcy] = true; q.push(cur); while (!q.empty()) { cur = q.front(); q.pop(); for (i=0; i<4; i++) { next.x = cur.x + dir[i][0]; next.y = cur.y + dir[i][1]; //越界 if (next.x<0 || next.x>=m || next.y<0 || next.y>=n || tmap[next.x][next.y]=='X' || visited[next.x][next.y]) continue; ch = tmap[next.x][next.y]; if (ch == 'G') //目标 return true; visited[next.x][next.y] = true; if (ch == '.') { q.push(next); } else if (ch>='a' && ch<='e') { keyfound[ch-'a']++; q.push(next); } else if (ch>='A' && ch<='E' && keyfound[ch-'A']>=keynum[ch-'A']) { q.push(next); } } } return false; } int main() { int i, j, k; while (cin>>m>>n && m && n) { memset(keynum, 0, sizeof(keynum)); for (i=0; i<m; i++) for (j=0; j<n; j++) { cin >> tmap[i][j]; if (tmap[i][j]>='a' && tmap[i][j]<='e') keynum[tmap[i][j]-'a']++; else if (tmap[i][j]=='S') { srcx = i; srcy = j; } } memset(opened, 0, sizeof(opened)); while (true) { memset(visited, 0, sizeof(visited)); memset(keyfound, 0, sizeof(keyfound)); if (bfs()) //bfs搜集钥匙, 如果找到目标，输出YES { cout << "YES" << endl; break; } else //看有没有门可以被打开 { bool have = false; for (i=0; i<5; i++) { if (keyfound[i]>=keynum[i] && !opened[i]) //没开过的门 { have = true; opened[i] = true; for (j=0; j<m; j++) for (k=0; k<n; k++) { if (tmap[j][k] == 'A'+i) //开门, 将门换成'.' tmap[j][k] = '.'; } } } if (!have) { cout << "NO" << endl; break; } } } } return 0; }